1. Field of the invention
The invention relates to a system comprising an integrating digital signal processing device for processing a sequence of binary coded signal samples x(nT) which occur at a specified input sampling period T, for generating a sequence of binary coded signal samples z(mrT) which occur at a specified output sampling period rT, r being a positive integral.
Such a system may, for example, be used for converting a delta (DM) of differential pulse code (DPCM) modulated signal to a pulse code modulated (PCM) signal. To this end the DM or DPCM must first be decoded which results in integrating the DM pulses or the DPCM pulse groups. The signal samples supplied by the decoder are usually fed, through a filter for band width limitation, to a PCM coder which supplies binary coded signal samples with a sampling frequency which is considerably lower, for example a factor 8, than the sampling frequency of the DM or DPCM signal.
A system as described above may also comprise a non-recursive digital filter in which weighting factors are used which have been obtained by differential coding of the pulse response of the filter, for example, as described in U.S. Pat. No. 3,965,338 or as described by G. B. Lockhart in his article "Binary transversal filter with quantized coefficients;" Electronics Letters; June 3, 1971; Vol. 71, Nr. 11. To obtain the signal sample z(mrT) the binary coded signal samples which are supplied by the said non-recursive digital filter must yet be processed (integrated) in the integrating signal processing device.
2. Description of the state of the art
A known integrating signal processing device is formed by an accumulator in which a binary coded signal sample applied to, it is each time added to the so-called contents of the accumulator, this sum constitutes the new contents of the accumulator.
Another known embodiment of an integrating signal processing device is formed by means of a first-order recursive digital filter, in which a weighting factor W is used in the recursive part.
To obtain a signal sample z(mrT) at the output of the accumulator or the first-order recursive digital filter the contents thereof is each time read-out at a period T under the control of a clockpulse.
In this manner the first-order recursive digital filter supplies, for example, a signal sample z(mrT) whose relation to the input signal samples x(nT) of the filter is expressed by the equation. ##EQU1##
In this equation:
T: is the sampling period of the signal samples x(nT); PA0 i: is the number of the signal sample x(iT) occurring after the instant t=O; PA0 W: is the above said weighting factor; PA0 r: is a positive integer which indicates the output sampling period increase with respect to the input sampling period of the integrating digital signal processing device (r is assumed to exceed one); PA0 m: is a positive integer, which indicates the number of the signal samples z(mrT) which occurs after the instant t=O and at an integral multiple of the output sampling period rT.